The present invention relates to an engine immobilizer operative with an electronically controlled engine, and more specifically to detection of actual engine running conditions in order to re-arm the immobilizer.
Use of automotive vehicle security systems employing RF-interrogated transponders has become widespread. Transponders may typically be embedded in the head of a key with a shank for operating a standard mechanical lock on a steering column, for example. Each transponder has a unique digital security code which is transmitted to a vehicle security module and then compared to authorized codes stored within the vehicle security module. The security module may be a stand-alone module or may be more typically incorporated into an electronic engine control module which performs the engine control functions and executes an appropriate engine control strategy.
The engine immobilizer function includes an armed state and a disarmed state as determined by immobilizer software executed within the security module. In the armed state, the engine is disabled by preventing engine control functions from operating (e.g., by disabling the spark distribution system and/or the fuel injection system). In the disarmed state, the engine is not disabled and engine control functions are permitted to proceed.
When the ignition switch of the vehicle is turned off, power is normally removed from the security module. When power is then re-applied to the security module, the immobilizer initializes in the armed state so that the vehicle cannot be operated until a transponder has been interrogated and a matching unique security code has been detected. In response to the match, the immobilizer enters the disarmed state.
In order to ensure continued safe operation of a vehicle, the events which lead to a re-arming of the immobilizer (i.e., switching to the armed state) must be carefully considered. For example, re-arming could occur based upon monitoring of the position of the ignition switch so that the immobilizer would be re-armed upon detection of the ignition switch being put in the off position. However, a fault in the conductor line for monitoring ignition switch position might cause a re-arming and disabling of the engine at a time when the engine should otherwise continue operating. Thus, prior art security modules have instead re-armed based upon actual switching off of power to the module.
On the other hand, a fault may occur which prevents switching off of power to the security module, even though the ignition switch has been turned off and the operator has left the vehicle. For example, many electronic engine control modules are supplied power from a power relay (either electromechanical or fully electronic switching) which is driven from the ignition switch. If the relay becomes stuck on (e.g., a frozen solenoid or a short-circuited transistor), power may be continuously supplied to the electronic engine control. If the immobilizer function is contained in the electronic engine control module, then the immobilizer function may fail to re-arm. Since other critical engine components such as fuel injectors may receive their power by means other than the power relay for the electronic engine control module, the engine may still stop so that the operator does not notice anything unusual when shutting off the engine and leaving the vehicle. In other words, the driver turns off the ignition switch and the vehicle engine stops because a critical engine component other than the engine control module loses power. However, the electronic engine control module merely detects a stall condition and does not re-arm the immobilizer.
The engine immobilizer function may also be implemented within a separate security module which is in communication with the engine control module. Such a separate security module may have its power supplied through a relay and would be subject to the same problem.